1. Field of the Invention
The field of the invention is that of phase recovery devices for receivers in digital transmission systems.
2. Description of the Prior Art
The invention has been developed in the context of a half-duplex digital transmission system in which a receiver receives frames at regular intervals, which makes it necessary to recover the phase of a local clock at the frame frequency whose period is a high multiple of the local bit clock period.
There are various known synchronization methods applicable to signals of this type.
The known solutions usually effect synchronization by detecting the first bit of each frame received or by detecting a specific frame synchronization pattern. This pattern may consist in a violation of the code used to transmit the signal, for example.
Detecting the first received frame bit has the disadvantage of being highly sensitive to noise. On the other hand, the need to use a specific synchronization pattern involves a penalty in terms of throughput (data signalling rate) and additional complexity in the transmit-receive systems.
An object of the present invention is to alleviate the disadvantages of existing systems.
In more precise terms, a first object of the invention is to provide a synchronization system, in particular a frame synchronization system for a receiver which receives frames at regular intervals, which is easy to implement and which is highly immune to noise but offers high sensitivity for frame frequency acquisition.
Another object of the invention is to provide a synchronization device of this kind which, for some types of transmitted signal code at least, make it possible to avoid the use of a specific synchronization pattern in the transmitted signal.
An additional object of the invention is to provide a synchronization system which produces a pertinent phase difference indication which can be used, for example, to apply phase correction in a phase-locked loop external to the device in accordance with the invention.